1. Field of Invention
This invention relates in general to battery monitoring systems, and more specifically, to a method to detect battery stratification.
2. Background of Related Art
Vehicle systems utilize a vehicle battery to initially provide electrical energy for starting the vehicle's powertrain system. After the start of the powertrain system, an alternator is utilized as a primary source of energy for providing electrical energy to various electrical devices of the vehicle which prevents drainage of energy from the vehicle battery. In addition, the alternator provides electrical energy to the vehicle battery for recharging the vehicle battery for maintaining a substantially maximum voltage.
The vehicle battery is an electrochemical device that produces and stores electricity. The battery produces a DC current that flows in only one direction. When the battery is discharged, the battery changes the chemical energy to electrical energy. When the battery is charging, the electrical energy is converted into chemical energy for storing energy until needed. The battery is recharged via the alternator once the engine is started. Discharging occurs during vehicle cranking where current is drawn from the battery, when the battery is not utilized for a prolonged period of time, and when loads from the vehicle are present that require more energy than that which the alternator can supply.
A battery includes a plurality of cells having a negative plate and a positive plate within a container immersed in an electrolyte (e.g., SO4H2—sulfuric acid and water). Battery plates are typically made of lead and lead oxide. The plates act as dissimilar metals.
Under normal conditions, the battery transforms the chemical energy into electrical energy by means of a chemical reaction between the electrolyte SO4H2 and the lead of the plates. During the energy conversion and discharge of electrical energy from the battery, the acid reacts with the lead of the plates to build up the lead sulfate (SO4Pb2) which can shorten the life of a battery if not removed. This reaction is reversible, meaning that the lead sulfate can be converted back to sulfuric acid and water if electrolyte solution is remixed. Remixing typically is performed by providing the battery with an increased battery charge.
When a load is connected across the terminals, there is a current flow of electrons to equalize the difference in the charges on the plates. Excess electrons flow from the negative plate to the positive plate. During this flow, the plates can be measured by the poles of the battery to determine the voltage. The voltage depends on the concentration of acid solution and the lead (Pb) content of the battery plates with respect to the other plates.
If the electrolyte solution is stratified, the acid is denser than the water and is being layered on the bottom of the battery. Under this condition, the acid concentration is light on the top of the solution and heavier on the bottom of the solution. The high acid concentration on the bottom artificially raises an open circuit voltage and the battery voltage appears to be fully charged and operable, but in reality, it has a low cold cranking amperage (CCA). CCA is defined as the amount of current available that the battery can deliver for defined duration of time (e.g., typically rated at 30 seconds) at cold temperatures (e.g., 0° F./−18° C.) while maintaining a terminal to terminal voltage of about 7.2 volts or 1.2 volts per cell.
If this battery stratification is not detected and not corrected, then the further battery usage will result in lower storage capacity and degradation of the battery cells, and thereafter, irreversible damage to the battery.